Ion Heat Flux Instability in High-β, Weakly Collisional, Magnetized Plasma

High-β plasmas can be highly magnetized (ρ/H ≪ 1) at the largest astro-physical scales, e.g., in the intracluster medium (ICM) of galaxy clusters. If the plasma is furthermore weakly collisional, the transport of momentum and heat is highly anisotropic with respect to the magnetic field direction. In thermally stratified plasmas at sufficiently high β, the parallel heat flux can be large enough to trigger a kinetic ion heat flux instability, which back-reacts on the transport by deforming the field lines on ion-Larmor scales. In this work, we use the hybrid particle-in-cell code PEGASUS++ to calculate the steady-state heat flux through a stratified, high-β, collisionless, magnetized plasma. By tracking a large sample of ions and simulating across a range of β and temperature gradient length scales, we calculate the effective collision operator for ion heat-flux-driven wave turbulence and use it to solve the Chapman-Enskog-Braginskii problem. We discuss the implications of our results for the electron heat flux whistler instability and magneto-thermal convection in general.